1. Field of the Invention
The present invention relates to logo units used for displaying images such as for advertising, and particularly to an electrically illuminated logo unit.
2. Description of the Prior Art
A conventional logo unit, such as a registration mark on a billboard or an insignia on a vehicle, cannot illuminate itself. If the image of the logo unit is to be clearly seen at night, it must be illuminated by a light source, which is usually an external light source. However, external illumination has various inherent limitations, including the angle of illumination, the brightness of the source, and the reflective ratio of the logo unit. These limitations frequently result in the logo unit being unevenly illuminated. Furthermore, the brightness and overall aesthetic display of the logo unit may be unsatisfactory.
Generally, to solve the above-described problems, an active light source is arranged at the back of the logo unit. A logo unit having an active light source arranged at the back thereof is known as an illuminated logo unit.
A conventional illuminated logo unit as disclosed in U.S. Pat. No. 6,174,075 is represented in FIGS. 4 and 5. The illuminated logo unit 1 includes a pattern body 12, a frame 16 arranged around a periphery of the pattern body 12, and a point light source 101 arranged at the back of the pattern body 12. The pattern body 12 is elliptical, and includes a pattern 121, a top surface 17, a cavity 18, and a bottom surface 19. The pattern 121 defines a projection surface (not labeled) on the bottom surface 19. The cavity 18 is defined between the top surface 17 and the bottom surface 19. The point light source 101 is a light emitting diode (LED), and is secured in the cavity 18. In particular, the point light source 101 is arranged at a center of the projection surface defined on the bottom surface 19.
Because the point light source 101 is arranged at the center of the projection surface, the distribution of light energy over the whole projection surface from the point light source 101 is uneven. For example, a central circular area 100 of the pattern body 12 receives much more light energy from the point light source 101 than other portions of the pattern body 12. Accordingly, a brightness of the pattern 121 is not uniform. The result is that the overall pattern 121 cannot be clearly seen at night.